The present invention relates to a process for making alkyl esters of carboxylic acids via transesterification wherein the product alcohol is removed from the reaction mixture rapidly and efficiently thereby enhancing the rate of the reaction and the overall yield of ester.
It is well known that the product composition of a transesterification reaction is governed by equilibrium thermodynamics. Thus, in order to realize the maximum amount of product ester, the product alcohol should be removed as rapidly as possible in order to displace the position of the equilibrium in favor of the products. However, in manufacturing scale operations, such product alcohol removal is not easily achieved. For example, in the batch transesterification of a triglyceride with methanol to form fatty acid methyl esters, a triglyceride, methanol and sodium methoxide are added together and reacted at 75-80xc2x0 C. for one hour. The agitator is turned off and the mixture is allowed to settle. The glycerine layer will be on the bottom and is drained form the vessel. The agitator is turned on, additional sodium methoxide is added and the mixture is reacted for another hour at 75-80xc2x0 C., glycerine drained, the crude methyl ester is water washed and dried. In a continuous process, the triglyceride, methanol and catalysts are metered together using pumps and mixing is accomplished by pumping the mixture through a static mixer and long lengths of piping to a settling tank. In this tank, the mixture is pumped in on one side of the tank, the methyl esters are removed on the other side and the glycerine is drained from the bottom. Once the methyl esters leave this settling tank, they are further mixed with additional methanol and catalyst, pumped through a static mixer, pushed through piping and into a second settling tank. The methyl esters are pumped from this tank and further refined.
The foregoing example shows that the removal of glycerine, the product alcohol in the transesterification of a triglyceide, is not normally achieved rapidly. Thus, the rate of the product methyl ester formation is not as great as could be achieved were the glycerine removed as its is formed. Rapid removal of glycerine would result in more favorable economics.
In its most general aspect, the present invention pertains to a process for making an alkyl ester of a carboxylic acid via transesterification comprising the steps of: (1) reacting a carboxylic acid ester with an alcohol and an effective amount of a transesterification catalyst in a reaction zone to form a reaction mixture comprised of a product ester and a product alcohol; (2) passing the reaction mixture from step (1) through a centrifugal separation zone wherein the second alcohol is separated from the second ester. The process according to the invention allows for shorter reaction times and improved product yields.